Controllable electric discharge device



, July 15, 1941. E A. ET'ZRODT 2,249,604

CONTROLLABLE ELECTRIC DISCHARGE DEVICE Filed May 2, 1941 ATTORNEYPatente d July 15, 1941 V UNITED STATE].

CONTROLLABLE ELECTRIC DISCHARGE I DEVICE.

Adalbert Etzrodt, Berlin-Siemensstadt, Germany,

assignor to walt'ung und Fides Gesellschaft fiir die Ver- Verwertung von'gewerblichen' Schutzrechten mit =beschriinkter Haftung, Berlin,Germany, a corporation of Germany Application May 2, 1941, Serial No.391,498:

In Germany August 21, 1939 6 Claims.

The invention relates to gaseous discharge devices, and particularly tosuch devices permitting current to reverse its direction through thedevices.

An object of the temperature of the control electrode from reach-vingtoohighavalue' v Anotherobject of the inventionv is vtqspace'. thecontrol electrode or gridas far fromthe'main electrodes as possible. v p

A stillfurther object of the, invention is to limit the intersection ofthe discharge path of both directions of vcurrent flow to that of theintersectlons of two cones. V

Other objects and advantages of the invention will be apparent fromthefcllowingdescription and drawing, in which: I

Figure 1 is a cross-sectional view through a preferred embodiment oftheinvention.

Figure 2 is a top view of a modification oi the electrode structure ofFigure 1,

The present invention in its specific form, relates to a gas-filled orvapor-filled electric discharge vessel equipped with two electrodes,each capable of functioning alternately as acathode,

and as an anode, so that current can flow through the vessel in eitherdirection. In addition to those two main electrodes, there are providedone or mor control electrodes that have'to control the time-instants 'atwhich the ignition takes place,

invention .is to present. the

so that it becomes feasible, for instance, tocontrol in a simple mannerwith the aid of the discharge vessel in question, the mean value of analternating current that is caused to flow through the vessel. g a

The accuracy of the current-controlling efiect obtainable by means ofsuch a discharge vessel depends largely on the accuracy with which theignition can be produced .at the desired instants, In view hereof, it isquite important tosee to it that the temperature of the control gridwillnot become too high, for in the case of atoo high grid-temperature,thermionic emission bythe control grid would interfere in an undesiredmanner with the. discharge phenomena in the tube, Aside from ameasurewhich consists in properly choosing the material for and thedesigncharf acteristics of the control electrode proper, .there isanother effective measure for preventing, the grid temperature fromexceeding afcertain maximum value in 'a discharge vessel of; the tvrin-fcathode type that is being used as a current converter, and thismeasure consists in making the dis stances from the control gridtothemairi electrodesas large as possible. 'It has beeniound c oxidecoating. 7 H V trodes ans 'the'exhaust tube' 'li; are sealed by that itis especially advantageous to place the control grid at a suflicientlylarge distance from the main-electrode member that has to'functio'n asan anode. H

It is" known from experience, however, that large electrode-distances'lead to high firingvoltage values and to a strongly positive orientationof the ignitioncharacteristic. 'IIence it'i's not always advantageous orrecommendable-to" resort to the measure'of using large: ele'ctrodedistv, The presentinvention discloses how the difiiculties just referred tocan be avoided ina very simple manner. In accordance with thisinvention, the main and control electrodes of a gasfilled orvapor-filled electric discharge vessel which, equipped with at least onecontrol'electrode, will permit a flow of current iri either di motion,are so de signed'and so arranged with respect'to one another, that foreach one of the two directions of current flow, the 'dischargepath isessentially a cone-shaped surface which'intersects the cone-shapedsurface that constitutes the discharge path for the other direction ofcurrent flow. The vertex of' each cone-shaped surface is supposed to belocated on one of the main electrodes, or, more's'pecificallyjon thatportion of this electrode which constitutes the cathode'forthe'discharges'taking place along the surface in question, while thebase of thesurface islocat'dbn'the other main electrode; 'or;"inorespecifically, on that portion of this electrode which constitutestheanode for'said discharge. In order'to showmore clearly howthe'presen't invention can-find application in practicejrefeb ence willbe made in this description from now on to theexample of theapplicationillu'strated on the drawing; The latter shows a controllabledischarge device of the twin-cathode type, whose vess'l l is made ofmetal. Itis obvious, however, that the device could be provided equallyas well with a vessel made 'of insulating material.

Inside the vessel" are mounted the two main electrodes, and the controlelectrode: The .first main electrode 2 consists of a cathode member 3and an anode member 4. Similarly, the second main electrode 5 consistsof a cathode member '6 and n" anode member I. The anodes-maybe in theform of solid annulusstrips, or they may be ribbons of wire gauze whichare standing on edge in the direction of the discharge.

"The cathode members may be al h'eater wire. preferably covered with anelectron-emitting Thelead-in Wires for the elecfusion in plug-shapedglass bodies 9 and Ill. The control grid I I has several openings, twoof which, designated by I2 and I3, are visible on the drawing. Thelatter shows clearly the peculiar arrangement of the electrodes. Thedotted line I4 gives an approximate indication of the path following bya discharge taking place between cathode member 3 and anode member I.This discharge essentially follows the surface of a cone, whosegeneratrix is the dotted line I 4. The discharge in the oppositedirection essentially follows the surface of a cone whose generatrixis-the dotted line I5.

In place of the annulus for the anode in Figure l, the anode portion maybe segments, such as 20, 2|, 22, 23, 24 and 25 on the conductive base26. The location of these segments is determined by the place of impactof the conical discharge after passing through the openings I2.

It is readily seen from the drawing that by adopting an arrangement inaccordance withthe present invention, it-becomes feasible to mount theanode members close to the grid openings, which are preferably locatedon a circle, and to keep, at the same time, the cathode members at asafe distance from these openings.

In other words, it becomes feasible to lower considerably thetemperature of the grid without making the distance between anode'andgrid so large that the ignition voltage would be increased in anundesirable manner, and without incurring the other disadvantagesgenerally encountered when the distance between anode and grid is maderelatively large. Consequently, the ignitionvoltage ofthe dischargevessel will be low, the shape and orientation of the characteristic willbe favorable, and the functioning of the vessel will be very accurateand, at the same time, very reliable, because the grid temperature is solow that emission by the grid will not occur.

It is especially advantageous to locate the cen ters of the gridopenings on a circle, and to provide the anode in the form of anannulus, as has been done in the case of the example of application'shown on the drawing. At the same time, a shield IS, IT can be placedbetween the cathode member and the anode member of each main electrode,in order thatthe emissivity of the cathode will not be affected 'by thepersistent fluctuations in anode temperature which fluctuations are dueto the alternating character of the loading conditions. r

The shape adopted for the anodes used in the discharge vessel, shown onthe drawing, is also advantageous from the standpoint of heat removal.The controlling effect of the anode members 4 and I, originates on thering-shaped portions of these members which are very close to the gridopenings. On the other hand, the discharge, which is the source of thegenerated heat, is free to spread out immediately and cover surfaceportions of the anode members, which are located at greater distancesfrom the grid openings, and which, for this reason, will have a lessdangerous influence on the grid temperature. Moreover, the heat absorbedby the anode from the discharge, will be rapidly transferred to the longexternal outer wall of the anode so that, because .of the large surfacearea of this wall, said heat can readily flow off into the surroundingspace in the form of radiant energy.

The distances between the various electrodes must be chosen depending onthe conditions under which the vessel must operate, that is, de-

pending on the magnitude of the voltages and currents. In general, itwill be advantageous to make the distance between the cathode member ofeach main electrode and the grid, from three to five times as large asthe distance between the anode member of each main electrode and thegrid.

When the discharge vessel in' question is used in practice, it is oftenobserved, although sometimes not until after the vessel has beenoperating for a considerable length of time, that in passing through thecontrol grid, the discharge displays a certain preference for certaingrid openings, insofar as it will pass almost exclusively through theseparticular openings, and not through the others. In order to suppressthis tendency, it will be advantageous to shape and to arrange the anodemembers of the main electrodes in such a manner as to make that thepulling effect of each anode, with respect to a given group of gridopenings, will be stronger than the pulling effect of the same anodewith respect to the other grid openings.

This can be done in a very simple manner by providing, for instance, theanode members 4 and 1, not in the form offull rings, as in Figure 1, butin the form of ring segments, as in Figure 2. These ring segments aremounted in such positions that the anode member of the first mainelectrode will be located close to one group of grid openings, while theanode member of the second main electrode will be located close toanother group of grid openings. The grid member I I may have sixopenings for the six segments disclosed in Figure 2, and another sixopenings forthe segments of the other anode portion, whose segmentswould be 30 displaced from the segments of the first anode portion.Various other arrangements may be utilized, such as having an anodeportion on one semi-circle on one electrode, and on the othersemi-circle on the other electrode.

These constructions just described will have the consequence that whenthe discharge takes place in one direction, it will always pass throughthe first group of grid' openings, while a discharge taking place in theopposite direction will always pass through the second groups of gridopenings. It has been found that when this measure is taken, the life ofthe discharge vessel will be lengthened, while its controllingcharacteristics will be improved.

I claim:

1. A discharge device having an envelope containing two composite mainelectrodes, each having an anode portion and a cathode portion, thecathode portion having a central position. and the anode portion inannular relation with said cathode portion, and a single controlelectrode intermediate said main electrodes.

2. A discharge device having an envelope containing two composite mainelectrodes, each having an anode portion and a cathode portion, thecathode portion having a central position and the anode portion inannular relation with said cathode portion, and a single controlelectrode intermediate said main electrodes, said control electrodecomprising a plate with openings arranged in an annular path.

3. A dischargedevice comprising an envelope having a cathode located ina central portion at one end of the envelope, .an annular anodeat theother end of the envelope, and an intermediate control electrode withannularly arranged openings therein whereby the discharge path from saidcathode to said anode is substantially in the form of a cone.

4. A discharge device comprising an envelope containing two compositemain electrodes, each having a central cathode portion and an annularanode portion surrounding said cathode portion whereby the dischargepath from the cathode portion of one electrode to the anode portion ofthe other electrode is in the shape of a cone, and a control electrodeintermediate said main electrodes and having discharge openings at theintersection of said discharge path cones.

5. A discharge device having an envelope containing two composite mainelectrodes, each having an anode portion and a cathode portion, the

cathode portion having a central position and the anode portion inannular relation with said cathode portion, and a heat shieldintermediate the cathode and anode portions of each electrode.

6. A composite electrode for discharge devices, comprising a centralcathode coil, a conducting base connected to one end of said coil, aconnection to the other end of said coil passing through said base,insulation between said connection and said base, a heat shield arrangedaround said coil and an annularly shaped anode portion around saidshield and coil on said base.

ADALBERT ETZRODT.

